Problem: In language class, the girl to boy ratio is $9$ to $4$. If there are a total of $26$ students, how many girls are there?
Answer: A ratio of $9$ girls to $4$ boys means that a set of $13$ students will have $9$ girls and $4$ boys. A class of $26$ students has $2$ sets of $13$ students. Because we know that there are $9$ girls in each set of $13$ students, the class must have $2$ groups of $9$ girls each. There is a total of $18$ girls in language class.